pointer functions - nebie question

Hi all
say I have this function:
char *trim(char *string)

If I understand it correctly the function's result value has to be allocated, let's say, by malloc. But how is this allocation going to be freed? All I do in my program is this:

string = trim(string)

Thanks in advance

Here is the function

Code:

---

char *
trim (char *string)
{
  char *result = 0;

  /* Ignore NULL pointers.  */
  if (string)
    {
      char *ptr = string;

      /* Skip leading whitespace.  */
      while (strchr (WHITESPACE_STR, *ptr))
        ++ptr;

      /* Make a copy of the remainder.  */                   
      if ((result = (char *) malloc(strlen(ptr)+1)) == NULL) 
    {                                                       
        fprintf(stderr,"trim() - Cannot allocate; %s",ptr);   
        return NULL;                                         
    }                                                       
    memset(result,'\0',strlen(ptr)+1);                     
    strcpy(result,ptr);                                     

      /* Move to the last character of the copy.  */
      for (ptr = result; *ptr; ++ptr)
        /* NOWORK */;
      --ptr;

      /* Remove trailing whitespace.  */
      for (--ptr; strchr (WHITESPACE_STR, *ptr); --ptr)
          *ptr = '\0';
  }

  return result;
}

---

The calling function would have to free() the memory. Alternatively, you could pass a buffer to your trim() function in which the trimmed string is stored. Or, if you're not concerned with keeping a pure copy of the string you could just hack up the original string in the function.

free(string);

I guess it wouldn't be a good design for the calling function to free memory that was allocated in the called function. Since the trimmed value could not be bigger than the *string parameter, I will free the allocated memory in the trim function itself and copy the result value back to the string parameter.

Thanks a lot